This invention relates to optical instruments for determining the amount of curvature of a surface and includes all specular surfaces from spherical to aspherical. Prior art instruments were concerned with measurement of predominantly spherical objects such as the cornea of the eye, or shapes such as ball bearings. This invention is concerned with measurement of the curvature of surfaces such as parabolas and hyperbolas. Prior art instruments for measuring curvature cannot accommodate optical elements having large numerical apertures nor parabolic or hyperbolic surfaces.